1. Field of the Invention
The present invention relates to a solid state image sensor. More particularly, the present invention relates to a solid state image sensor to be used for a digital still camera a digital video camera, etc.
2. Description of the Related Art
Currently, polarization filters are being employed to acquire or remove polarization information in a digital still camera or a digital video camera.
For example, a polarization filter is fitted to the lens of a camera in order to attenuate unnecessary reflected light that arises at an interface such as a glass surface or a water surface and an image is picked up by removing specific polarized light.
With optical interferometric measurement, an interference image having a specific phase difference is acquired by adjusting a polarization filter.
In either case, a polarization filter is inserted into a front face of a solid state image sensor to detect polarization information, because the solid state image sensor detects only luminance information of light but cannot acquire polarization information.
Then, the entire solid state image sensor receives only light transmitted through the polarization filter. Therefore, if plural pieces of polarization information are required, the solid state image sensor is required to operate plural times to pick up images.
If a solid state image sensor can detect plural pieces of polarization information, the solid state image sensor can acquire polarization information on an image of a subject without using a polarization filter.
Japanese Patent Application Laid-Open No. 2007-086720 proposes a technique of using a polarization filter array made of photonic crystal and arranged on the pixels of a solid state image sensor for the purpose of making the solid state image sensor able to detect plural pieces of polarization information.
However, a polarization filter array made of photonic crystal as described in Japanese Patent Application Laid-Open No. 2007-086720 cannot be fabricated with a size of several micrometers that is substantially equal to the size of downsized small pixels that have become popular in recent years. Additionally, the number of periods in a photonic crystal is small, hence resulting in poor polarization splitting characteristics.
Additionally, the process of manufacturing a solid state image sensor equipped with a polarization filter array requires additional steps relative to a conventional process for precisely aligning a polarization filter array with the pixels of the solid state image sensor, which can be conducted only with difficulty, hence resulting in high manufacturing cost.